Methyl mercury is considered to be a developmental neurotoxicant. However, contrary to expected findings, a longitudinal study in the Seychelles has revealed a positive association between increasing mercury levels, measured in maternal hair prenatally and in infant hair, and enhanced child development. Given that fish consumption the Seychelles is high, and that fish intakes correlate with hair mercury levels, we hypothesize that certain micronutrients in fish may be (a) beneficial the child development and (b) protective against the neurotoxic effects of methyl mercury. We propose to test this hypothesis in a new study of 250 mother-infant pairs recruited in the Seychelles during the first trimester and followed longitudinally until the infants reach 29 months of age using the most sensitive developmental endpoints available. The four likely micronutrients, based on their levels in fish and their documented roles in brain development and prioritized in terms of biological plausibility, are the long chain polyunsaturated fatty acids principally docosahexaenoic acid, iodine, iron and the amino acid taurine. Also, selenium may play a role as a modifier of the toxic action of methyl mercury and, as such, will be included with mercury as an independent variable. Mercury in maternal and infant hair will continue to be used as our primary measure of prenatal and post natal exposures. In addition to direct measures of mercury, micronutrient status and selenium levels in biological samples from mother and infant, a diet survey including fish consumption will be made at selected pre- and postnatal stages of this study. These data will allow us to characterize metabolic interrelationship between fish intake and levels of mercury and micronutrients that should further test the plausibility of our hypothesis. This proposed study should break new scientific grounds on the interrelationship between nutrition and toxicology. Specifically, we expect that data emanating from the project to indicate that nutritional variables must be taken into account in any evaluation of the neurotoxicity of methyl mercury when fish is the principal source of human exposure to mercury.